function add(a,b) {
    let maxLength = Math.max(a.length,b.length);
    a = a.padStart(maxLength,0)
    b = b.padStart(maxLength,0)
    let f = 0;
    let t = 0;
    let sum = "";
    for (let i = maxLength; i > 0 ; i--) {
        t = parseInt(a[i]+b[i]) + f;
        f = Math.floor(t/10)
        sum = sum + f
        
    }
}